2 * Copyright 2014-present Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
16 #ifndef __STDC_FORMAT_MACROS
17 #define __STDC_FORMAT_MACROS
20 #include <folly/io/async/EventBase.h>
28 #include <folly/Memory.h>
29 #include <folly/io/async/NotificationQueue.h>
30 #include <folly/io/async/VirtualEventBase.h>
31 #include <folly/portability/Unistd.h>
32 #include <folly/synchronization/Baton.h>
33 #include <folly/system/ThreadName.h>
38 * EventBase::FunctionRunner
41 class EventBase::FunctionRunner
42 : public NotificationQueue<EventBase::Func>::Consumer {
44 void messageAvailable(Func&& msg) noexcept override {
45 // In libevent2, internal events do not break the loop.
46 // Most users would expect loop(), followed by runInEventBaseThread(),
47 // to break the loop and check if it should exit or not.
48 // To have similar bejaviour to libevent1.4, tell the loop to break here.
49 // Note that loop() may still continue to loop, but it will also check the
50 // stop_ flag as well as runInLoop callbacks, etc.
51 event_base_loopbreak(getEventBase()->evb_);
54 // terminateLoopSoon() sends a null message just to
55 // wake up the loop. We can ignore these messages.
62 // The interface used to libevent is not thread-safe. Calls to
63 // event_init() and event_base_free() directly modify an internal
64 // global 'current_base', so a mutex is required to protect this.
66 // event_init() should only ever be called once. Subsequent calls
67 // should be made to event_base_new(). We can recognise that
68 // event_init() has already been called by simply inspecting current_base.
69 static std::mutex libevent_mutex_;
75 EventBase::EventBase(bool enableTimeMeasurement)
76 : runOnceCallbacks_(nullptr)
82 , avgLoopTime_(std::chrono::seconds(2))
83 , maxLatencyLoopTime_(avgLoopTime_)
84 , enableTimeMeasurement_(enableTimeMeasurement)
85 , nextLoopCnt_(uint64_t(-40)) // Early wrap-around so bugs will manifest soon
86 , latestLoopCnt_(nextLoopCnt_)
89 , observerSampleCount_(0)
90 , executionObserver_(nullptr) {
93 std::lock_guard<std::mutex> lock(libevent_mutex_);
95 // The value 'current_base' (libevent 1) or
96 // 'event_global_current_base_' (libevent 2) is filled in by event_set(),
97 // allowing examination of its value without an explicit reference here.
98 // If ev.ev_base is nullptr, then event_init() must be called, otherwise
99 // call event_base_new().
100 event_set(&ev, 0, 0, nullptr, nullptr);
107 evb_ = event_base_new();
110 if (UNLIKELY(evb_ == nullptr)) {
111 LOG(ERROR) << "EventBase(): Failed to init event base.";
112 folly::throwSystemError("error in EventBase::EventBase()");
114 VLOG(5) << "EventBase(): Created.";
115 initNotificationQueue();
118 // takes ownership of the event_base
119 EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
120 : runOnceCallbacks_(nullptr)
127 , avgLoopTime_(std::chrono::seconds(2))
128 , maxLatencyLoopTime_(avgLoopTime_)
129 , enableTimeMeasurement_(enableTimeMeasurement)
130 , nextLoopCnt_(uint64_t(-40)) // Early wrap-around so bugs will manifest soon
131 , latestLoopCnt_(nextLoopCnt_)
134 , observerSampleCount_(0)
135 , executionObserver_(nullptr) {
136 if (UNLIKELY(evb_ == nullptr)) {
137 LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
138 throw std::invalid_argument("EventBase(): event base cannot be nullptr");
140 initNotificationQueue();
143 EventBase::~EventBase() {
144 std::future<void> virtualEventBaseDestroyFuture;
145 if (virtualEventBase_) {
146 virtualEventBaseDestroyFuture = virtualEventBase_->destroy();
149 // Keep looping until all keep-alive handles are released. Each keep-alive
150 // handle signals that some external code will still schedule some work on
151 // this EventBase (so it's not safe to destroy it).
152 while (loopKeepAliveCount() > 0) {
153 applyLoopKeepAlive();
157 if (virtualEventBaseDestroyFuture.valid()) {
158 virtualEventBaseDestroyFuture.get();
161 // Call all destruction callbacks, before we start cleaning up our state.
162 while (!onDestructionCallbacks_.empty()) {
163 LoopCallback* callback = &onDestructionCallbacks_.front();
164 onDestructionCallbacks_.pop_front();
165 callback->runLoopCallback();
170 DCHECK_EQ(0u, runBeforeLoopCallbacks_.size());
172 (void)runLoopCallbacks();
174 if (!fnRunner_->consumeUntilDrained()) {
175 LOG(ERROR) << "~EventBase(): Unable to drain notification queue";
178 // Stop consumer before deleting NotificationQueue
179 fnRunner_->stopConsuming();
181 std::lock_guard<std::mutex> lock(libevent_mutex_);
182 event_base_free(evb_);
185 for (auto storage : localStorageToDtor_) {
186 storage->onEventBaseDestruction(*this);
189 VLOG(5) << "EventBase(): Destroyed.";
192 size_t EventBase::getNotificationQueueSize() const {
193 return queue_->size();
196 void EventBase::setMaxReadAtOnce(uint32_t maxAtOnce) {
197 fnRunner_->setMaxReadAtOnce(maxAtOnce);
200 void EventBase::checkIsInEventBaseThread() const {
201 auto evbTid = loopThread_.load(std::memory_order_relaxed);
202 if (evbTid == std::thread::id()) {
206 // Using getThreadName(evbTid) instead of name_ will work also if
207 // the thread name is set outside of EventBase (and name_ is empty).
208 auto curTid = std::this_thread::get_id();
209 CHECK(evbTid == curTid)
210 << "This logic must be executed in the event base thread. "
211 << "Event base thread name: \""
212 << folly::getThreadName(evbTid).value_or("")
213 << "\", current thread name: \""
214 << folly::getThreadName(curTid).value_or("") << "\"";
217 // Set smoothing coefficient for loop load average; input is # of milliseconds
218 // for exp(-1) decay.
219 void EventBase::setLoadAvgMsec(std::chrono::milliseconds ms) {
220 assert(enableTimeMeasurement_);
221 std::chrono::microseconds us = std::chrono::milliseconds(ms);
222 if (ms > std::chrono::milliseconds::zero()) {
223 maxLatencyLoopTime_.setTimeInterval(us);
224 avgLoopTime_.setTimeInterval(us);
226 LOG(ERROR) << "non-positive arg to setLoadAvgMsec()";
230 void EventBase::resetLoadAvg(double value) {
231 assert(enableTimeMeasurement_);
232 avgLoopTime_.reset(value);
233 maxLatencyLoopTime_.reset(value);
236 static std::chrono::milliseconds
237 getTimeDelta(std::chrono::steady_clock::time_point* prev) {
238 auto result = std::chrono::steady_clock::now() - *prev;
239 *prev = std::chrono::steady_clock::now();
241 return std::chrono::duration_cast<std::chrono::milliseconds>(result);
244 void EventBase::waitUntilRunning() {
245 while (!isRunning()) {
246 std::this_thread::yield();
250 // enters the event_base loop -- will only exit when forced to
251 bool EventBase::loop() {
255 bool EventBase::loopOnce(int flags) {
256 return loopBody(flags | EVLOOP_ONCE);
259 bool EventBase::loopBody(int flags) {
260 VLOG(5) << "EventBase(): Starting loop.";
262 DCHECK(!invokingLoop_)
263 << "Your code just tried to loop over an event base from inside another "
264 << "event base loop. Since libevent is not reentrant, this leads to "
265 << "undefined behavior in opt builds. Please fix immediately. For the "
266 << "common case of an inner function that needs to do some synchronous "
267 << "computation on an event-base, replace getEventBase() by a new, "
268 << "stack-allocated EvenBase.";
269 invokingLoop_ = true;
271 invokingLoop_ = false;
275 bool ranLoopCallbacks;
276 bool blocking = !(flags & EVLOOP_NONBLOCK);
277 bool once = (flags & EVLOOP_ONCE);
279 // time-measurement variables.
280 std::chrono::steady_clock::time_point prev;
281 std::chrono::steady_clock::time_point idleStart = {};
282 std::chrono::microseconds busy;
283 std::chrono::microseconds idle;
285 loopThread_.store(std::this_thread::get_id(), std::memory_order_release);
287 if (!name_.empty()) {
288 setThreadName(name_);
291 if (enableTimeMeasurement_) {
292 prev = std::chrono::steady_clock::now();
296 while (!stop_.load(std::memory_order_relaxed)) {
297 applyLoopKeepAlive();
300 // Run the before loop callbacks
301 LoopCallbackList callbacks;
302 callbacks.swap(runBeforeLoopCallbacks_);
304 while(!callbacks.empty()) {
305 auto* item = &callbacks.front();
306 callbacks.pop_front();
307 item->runLoopCallback();
310 // nobody can add loop callbacks from within this thread if
311 // we don't have to handle anything to start with...
312 if (blocking && loopCallbacks_.empty()) {
313 res = event_base_loop(evb_, EVLOOP_ONCE);
315 res = event_base_loop(evb_, EVLOOP_ONCE | EVLOOP_NONBLOCK);
318 ranLoopCallbacks = runLoopCallbacks();
320 if (enableTimeMeasurement_) {
321 auto now = std::chrono::steady_clock::now();
322 busy = std::chrono::duration_cast<std::chrono::microseconds>(
324 idle = std::chrono::duration_cast<std::chrono::microseconds>(
325 startWork_ - idleStart);
326 auto loop_time = busy + idle;
328 avgLoopTime_.addSample(loop_time, busy);
329 maxLatencyLoopTime_.addSample(loop_time, busy);
332 if (observerSampleCount_++ == observer_->getSampleRate()) {
333 observerSampleCount_ = 0;
334 observer_->loopSample(busy.count(), idle.count());
338 VLOG(11) << "EventBase " << this << " did not timeout "
339 << " loop time guess: " << loop_time.count()
340 << " idle time: " << idle.count()
341 << " busy time: " << busy.count()
342 << " avgLoopTime: " << avgLoopTime_.get()
343 << " maxLatencyLoopTime: " << maxLatencyLoopTime_.get()
344 << " maxLatency_: " << maxLatency_.count() << "us"
345 << " notificationQueueSize: " << getNotificationQueueSize()
346 << " nothingHandledYet(): " << nothingHandledYet();
348 // see if our average loop time has exceeded our limit
349 if ((maxLatency_ > std::chrono::microseconds::zero()) &&
350 (maxLatencyLoopTime_.get() > double(maxLatency_.count()))) {
352 // back off temporarily -- don't keep spamming maxLatencyCob_
353 // if we're only a bit over the limit
354 maxLatencyLoopTime_.dampen(0.9);
357 // Our loop run did real work; reset the idle timer
360 VLOG(11) << "EventBase " << this << " did not timeout";
363 // If the event loop indicate that there were no more events, and
364 // we also didn't have any loop callbacks to run, there is nothing left to
366 if (res != 0 && !ranLoopCallbacks) {
367 // Since Notification Queue is marked 'internal' some events may not have
368 // run. Run them manually if so, and continue looping.
370 if (getNotificationQueueSize() > 0) {
371 fnRunner_->handlerReady(0);
377 if (enableTimeMeasurement_) {
378 VLOG(11) << "EventBase " << this << " loop time: " <<
379 getTimeDelta(&prev).count();
386 // Reset stop_ so loop() can be called again
387 stop_.store(false, std::memory_order_relaxed);
390 LOG(ERROR) << "EventBase: -- error in event loop, res = " << res;
392 } else if (res == 1) {
393 VLOG(5) << "EventBase: ran out of events (exiting loop)!";
394 } else if (res > 1) {
395 LOG(ERROR) << "EventBase: unknown event loop result = " << res;
399 loopThread_.store({}, std::memory_order_release);
401 VLOG(5) << "EventBase(): Done with loop.";
405 ssize_t EventBase::loopKeepAliveCount() {
406 if (loopKeepAliveCountAtomic_.load(std::memory_order_relaxed)) {
407 loopKeepAliveCount_ +=
408 loopKeepAliveCountAtomic_.exchange(0, std::memory_order_relaxed);
410 DCHECK_GE(loopKeepAliveCount_, 0);
412 return loopKeepAliveCount_;
415 void EventBase::applyLoopKeepAlive() {
416 auto keepAliveCount = loopKeepAliveCount();
417 // Make sure default VirtualEventBase won't hold EventBase::loop() forever.
418 if (virtualEventBase_ && virtualEventBase_->keepAliveCount() == 1) {
422 if (loopKeepAliveActive_ && keepAliveCount == 0) {
423 // Restore the notification queue internal flag
424 fnRunner_->stopConsuming();
425 fnRunner_->startConsumingInternal(this, queue_.get());
426 loopKeepAliveActive_ = false;
427 } else if (!loopKeepAliveActive_ && keepAliveCount > 0) {
428 // Update the notification queue event to treat it as a normal
429 // (non-internal) event. The notification queue event always remains
430 // installed, and the main loop won't exit with it installed.
431 fnRunner_->stopConsuming();
432 fnRunner_->startConsuming(this, queue_.get());
433 loopKeepAliveActive_ = true;
437 void EventBase::loopForever() {
441 applyLoopKeepAlive();
443 // Make sure notification queue events are treated as normal events.
444 // We can't use loopKeepAlive() here since LoopKeepAlive token can only be
445 // released inside a loop.
446 ++loopKeepAliveCount_;
448 --loopKeepAliveCount_;
454 folly::throwSystemError("error in EventBase::loopForever()");
458 void EventBase::bumpHandlingTime() {
459 if (!enableTimeMeasurement_) {
463 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__ <<
464 " (loop) latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
465 if (nothingHandledYet()) {
466 latestLoopCnt_ = nextLoopCnt_;
468 startWork_ = std::chrono::steady_clock::now();
470 VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__
471 << " (loop) startWork_ " << startWork_.time_since_epoch().count();
475 void EventBase::terminateLoopSoon() {
476 VLOG(5) << "EventBase(): Received terminateLoopSoon() command.";
478 // Set stop to true, so the event loop will know to exit.
479 stop_.store(true, std::memory_order_relaxed);
481 // Call event_base_loopbreak() so that libevent will exit the next time
483 event_base_loopbreak(evb_);
485 // If terminateLoopSoon() is called from another thread,
486 // the EventBase thread might be stuck waiting for events.
487 // In this case, it won't wake up and notice that stop_ is set until it
488 // receives another event. Send an empty frame to the notification queue
489 // so that the event loop will wake up even if there are no other events.
491 // We don't care about the return value of trySendFrame(). If it fails
492 // this likely means the EventBase already has lots of events waiting
495 queue_->putMessage(nullptr);
497 // We don't care if putMessage() fails. This likely means
498 // the EventBase already has lots of events waiting anyway.
502 void EventBase::runInLoop(LoopCallback* callback, bool thisIteration) {
503 dcheckIsInEventBaseThread();
504 callback->cancelLoopCallback();
505 callback->context_ = RequestContext::saveContext();
506 if (runOnceCallbacks_ != nullptr && thisIteration) {
507 runOnceCallbacks_->push_back(*callback);
509 loopCallbacks_.push_back(*callback);
513 void EventBase::runInLoop(Func cob, bool thisIteration) {
514 dcheckIsInEventBaseThread();
515 auto wrapper = new FunctionLoopCallback(std::move(cob));
516 wrapper->context_ = RequestContext::saveContext();
517 if (runOnceCallbacks_ != nullptr && thisIteration) {
518 runOnceCallbacks_->push_back(*wrapper);
520 loopCallbacks_.push_back(*wrapper);
524 void EventBase::runOnDestruction(LoopCallback* callback) {
525 std::lock_guard<std::mutex> lg(onDestructionCallbacksMutex_);
526 callback->cancelLoopCallback();
527 onDestructionCallbacks_.push_back(*callback);
530 void EventBase::runBeforeLoop(LoopCallback* callback) {
531 dcheckIsInEventBaseThread();
532 callback->cancelLoopCallback();
533 runBeforeLoopCallbacks_.push_back(*callback);
536 bool EventBase::runInEventBaseThread(Func fn) {
538 // It will be received by the FunctionRunner in the EventBase's thread.
540 // We try not to schedule nullptr callbacks
542 LOG(ERROR) << "EventBase " << this
543 << ": Scheduling nullptr callbacks is not allowed";
547 // Short-circuit if we are already in our event base
548 if (inRunningEventBaseThread()) {
549 runInLoop(std::move(fn));
554 queue_->putMessage(std::move(fn));
555 } catch (const std::exception& ex) {
556 LOG(ERROR) << "EventBase " << this << ": failed to schedule function "
557 << "for EventBase thread: " << ex.what();
564 bool EventBase::runInEventBaseThreadAndWait(Func fn) {
565 if (inRunningEventBaseThread()) {
566 LOG(ERROR) << "EventBase " << this << ": Waiting in the event loop is not "
572 runInEventBaseThread([&ready, fn = std::move(fn)]() mutable {
576 // A trick to force the stored functor to be executed and then destructed
577 // before posting the baton and waking the waiting thread.
578 copy(std::move(fn))();
585 bool EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(Func fn) {
586 if (isInEventBaseThread()) {
590 return runInEventBaseThreadAndWait(std::move(fn));
594 bool EventBase::runLoopCallbacks() {
595 if (!loopCallbacks_.empty()) {
597 // Swap the loopCallbacks_ list with a temporary list on our stack.
598 // This way we will only run callbacks scheduled at the time
599 // runLoopCallbacks() was invoked.
601 // If any of these callbacks in turn call runInLoop() to schedule more
602 // callbacks, those new callbacks won't be run until the next iteration
603 // around the event loop. This prevents runInLoop() callbacks from being
604 // able to start file descriptor and timeout based events.
605 LoopCallbackList currentCallbacks;
606 currentCallbacks.swap(loopCallbacks_);
607 runOnceCallbacks_ = ¤tCallbacks;
609 while (!currentCallbacks.empty()) {
610 LoopCallback* callback = ¤tCallbacks.front();
611 currentCallbacks.pop_front();
612 folly::RequestContextScopeGuard rctx(std::move(callback->context_));
613 callback->runLoopCallback();
616 runOnceCallbacks_ = nullptr;
622 void EventBase::initNotificationQueue() {
623 // Infinite size queue
624 queue_ = std::make_unique<NotificationQueue<Func>>();
626 // We allocate fnRunner_ separately, rather than declaring it directly
627 // as a member of EventBase solely so that we don't need to include
628 // NotificationQueue.h from EventBase.h
629 fnRunner_ = std::make_unique<FunctionRunner>();
631 // Mark this as an internal event, so event_base_loop() will return if
632 // there are no other events besides this one installed.
634 // Most callers don't care about the internal notification queue used by
635 // EventBase. The queue is always installed, so if we did count the queue as
636 // an active event, loop() would never exit with no more events to process.
637 // Users can use loopForever() if they do care about the notification queue.
638 // (This is useful for EventBase threads that do nothing but process
639 // runInEventBaseThread() notifications.)
640 fnRunner_->startConsumingInternal(this, queue_.get());
643 void EventBase::SmoothLoopTime::setTimeInterval(
644 std::chrono::microseconds timeInterval) {
645 expCoeff_ = -1.0 / timeInterval.count();
646 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
649 void EventBase::SmoothLoopTime::reset(double value) {
653 void EventBase::SmoothLoopTime::addSample(
654 std::chrono::microseconds total,
655 std::chrono::microseconds busy) {
656 if ((buffer_time_ + total) > buffer_interval_ && buffer_cnt_ > 0) {
657 // See https://en.wikipedia.org/wiki/Exponential_smoothing for
658 // more info on this calculation.
659 double coeff = exp(buffer_time_.count() * expCoeff_);
661 value_ * coeff + (1.0 - coeff) * (busy_buffer_.count() / buffer_cnt_);
662 buffer_time_ = std::chrono::microseconds{0};
663 busy_buffer_ = std::chrono::microseconds{0};
666 buffer_time_ += total;
667 busy_buffer_ += busy;
671 bool EventBase::nothingHandledYet() const noexcept {
672 VLOG(11) << "latest " << latestLoopCnt_ << " next " << nextLoopCnt_;
673 return (nextLoopCnt_ != latestLoopCnt_);
676 void EventBase::attachTimeoutManager(AsyncTimeout* obj,
677 InternalEnum internal) {
679 struct event* ev = obj->getEvent();
680 assert(ev->ev_base == nullptr);
682 event_base_set(getLibeventBase(), ev);
683 if (internal == AsyncTimeout::InternalEnum::INTERNAL) {
684 // Set the EVLIST_INTERNAL flag
685 event_ref_flags(ev) |= EVLIST_INTERNAL;
689 void EventBase::detachTimeoutManager(AsyncTimeout* obj) {
691 struct event* ev = obj->getEvent();
692 ev->ev_base = nullptr;
695 bool EventBase::scheduleTimeout(AsyncTimeout* obj,
696 TimeoutManager::timeout_type timeout) {
697 dcheckIsInEventBaseThread();
698 // Set up the timeval and add the event
700 tv.tv_sec = long(timeout.count() / 1000LL);
701 tv.tv_usec = long((timeout.count() % 1000LL) * 1000LL);
703 struct event* ev = obj->getEvent();
704 if (event_add(ev, &tv) < 0) {
705 LOG(ERROR) << "EventBase: failed to schedule timeout: " << strerror(errno);
712 void EventBase::cancelTimeout(AsyncTimeout* obj) {
713 dcheckIsInEventBaseThread();
714 struct event* ev = obj->getEvent();
715 if (EventUtil::isEventRegistered(ev)) {
720 void EventBase::setName(const std::string& name) {
721 dcheckIsInEventBaseThread();
725 setThreadName(loopThread_.load(std::memory_order_relaxed),
730 const std::string& EventBase::getName() {
731 dcheckIsInEventBaseThread();
735 const char* EventBase::getLibeventVersion() { return event_get_version(); }
736 const char* EventBase::getLibeventMethod() { return event_get_method(); }
738 VirtualEventBase& EventBase::getVirtualEventBase() {
739 folly::call_once(virtualEventBaseInitFlag_, [&] {
740 virtualEventBase_ = std::make_unique<VirtualEventBase>(*this);
743 return *virtualEventBase_;
746 constexpr std::chrono::milliseconds EventBase::SmoothLoopTime::buffer_interval_;